1. Field of the Invention
The present invention relates to a push button switch of the type in which it is turned on (or off) when a push button is pushed, and is turned off (or on) when the push button is pushed once more.
2. Related art
A push button switch constructed as shown in FIGS. 6 and 7 has been known for this type of the push button switch. In the construction of this conventional switch, a movable contact 2 is operated by a push button 1. The push button 1 includes a first inner surface 1a fit into a space defined by a guide wall 3a of a housing 3. A first spring 4 urging the push button 1 upward is within a space defined by the first inner surface 1a. A second inner surface 1b is further included by the push button 1. It Is located on the outer side of the first inner surface 1a. A sleeve (moving member) 5 is fit into a space defined by the second inner surface 1b of the push button 1. The movable contact 2 is mounted on the bottom surface of the sleeve 5. A fixed contact 6, located in opposition to the movable contact 2, is mounted on the inner side of the bottom of the housing 3.
A second spring 7 for urging the sleeve 5 downward is provided within a space defined by the second inner surface 1b. The second spring 7 is in a fully expanded state when the push button 1 is not depressed, i.e., the switch is in an off state. A force of the spring to urge the movable contact 2 toward the fixed contact 6 is zero. Under the sleeve 5, a cylindrical rubber contact 8 surrounds the movable contact 2. The rubber contact 8 functions such that when the urging force of the second spring 7 is substantially zero, it separates the movable contact 2 apart from the fixed contact 6 by its elastic force. A heart cam, not shown, is further included in the push button 1. A pin 9 operating along the outer surface of the heart cam is contained in the housing 3.
The heart cam is a plate-like cam of which the upper side includes and incurred part. When the push button 1 is depressed, the pin 9 moves upward along the outer circumference of the heart cam and is put in the incurved part of the heart cam, so that the push button 1 is held at a predetermined depth level. When the push button 1 is depressed again, the pin 9 disengages from the incurved part, thereby placing the push button 1 in a free state.
In the push button switch thus constructed, in a state that the push button switch is in an off state, when the push button 1 is depressed, the first and second springs 4 and 7 are compressed. At this time, the compressing force of the second spring 7 is larger than the holding force of the rubber contact 8, bringing the movable contact 2 into contact with the sleeve 5. Under this condition, the pin 9 is put at the incurred part of the heart cam, and the push button 1 is left depressed, i.e., an on state of the push button switch is maintained.
When the push button 1 is depressed once more, the first and second springs 4 and 7 are further compressed slightly, so that the pin 9 disengages from the incurred part of the heart cam. Then, the repulsive forces of the first and second springs 4 and 7 push the push button 1 upward. As a result, the second spring 7 is fully expanded, and the elastic force of the rubber contact 8 separates the movable contact 2 from the fixed contact 6, i.e., the push button switch is in an off state.
In the conventional push button switch thus constructed and operated, the push button i is movably assembled into the housing 3. The sleeve 5 is movably coupled with the push button 1. Accordingly, it can be considered that the sleeve 5 moves under a large tolerance A+B (A: fitting tolerance between the first inner surface 1a and the guide wall 3a, and B:fitting tolerance between the second inner surface 1b and the sleeve 5). In other words, when the push button 1 is depressed, the sleeve 5 moves in a greatly inclined state. The movable contact 2 comes in contact with the fixed contact 6 also in a greatly inclined state. Consequently, a poor contact problem tends to occur in the conventional push button switch.